Title

Identifier

Author

Degree

Doctor of Philosophy (PhD)

Department

Engineering Science (Interdepartmental Program)

Document Type

Dissertation

Abstract

Electrodeposited Au/CoAu multilayered nanowires are materials with alternating layers of Au and CoAu in a wire where the layer thickness and wire diameter are nanometer size. They can be used for different applications. For example, the wires may exhibit giant magnetoresistance (GMR), a change in the materials resistance with a magnetic field, having applications as a sensor material for microdevices. If Co is etched from CoAu nanowires, rough, porous gold nanostructures will be left behind, which could be used as novel catalysts. In this study, the electrodeposition of Au/CoAu multilayered nanowires and nanotubes in nanoporous templates was explored from a non-cyanide electrolyte. The multilayers were deposited with a pulse current control and the template pore size played an important role in determining whether nanowires or nanotubes were formed. The magnetic and magnetoresistive properties of Au/CoAu multilayered nanostructures were examined. Au/CoAu multilayered thin films exhibited both normal and inverse CIP GMR. After electrodeposition, the solid nanowires were released from the template and one component was electrochemically etched from the nanowires. The electrochemical etching conditions were predetermined by the investigation of electrochemical etching behavior of CoAu alloy and pure Co thin films. By precisely controlling the electrochemical etching potential and time, the surface area of the nanowires was enhanced. Nano-bamboo structures were created after partial etching and Au nanodisk structures were created after complete etching. Compared to conventional chemical etching, the anodization etching process presented here can be controlled to produce partially etched structures. The anodization process was monitored by two techniques. The current was recorded during etching and the total charge was proportional to the layer size. In addition, cyclic voltammetry (CV) was used as a way to observe the partial etching of the nanowires. In addition, the annealing post-treatment was tested to enhance the magnetoresistive properties of Au/CoAu multilayered nanostructures and to improve the quality of the multilayer interface by promoting phase segregation. Furthermore, hollow nano-bamboo structure and ordered nanorings with various aspect ratios were developed through the electrochemical etching of Au/CoAu nanotubes in a similar way. To the best of the author’s knowledge, this has not been done before.